1. Field of the Invention
The present invention relates to a differential-to-single-ended converter and a phase-locked loop circuit having the same, and more particularly to a differential-to-single-ended converter having reduced power consumption and excellent duty ratio characteristics and a phase-locked loop circuit having the same.
2. Description of the Related Art
A differential-to-single-ended (D2S) converter located in a latter part of a voltage-controlled oscillator (VCO) may have a large influence on characteristics of a phase-locked loop (PLL) circuit. For example, the D2S converter has a significant effect on a duty ratio of an output signal, an operating voltage range, and power consumption in the PLL circuit. The operating voltage range and power consumption in the PLL circuit, respectively, have a trade-off relationship with each other.
FIG. 1 is a circuit diagram illustrating a conventional D2S converter.
Referring to FIG. 1, the D2S converter includes an amplification terminal configured with an N-type metal-oxide semiconductor (NMOS) transistor MN1 and P-type MOS (PMOS) transistors MP1 and MP2, and another amplification terminal configured with an NMOS transistor MN2 and PMOS transistors MP3 and MP4. An output current of the PMOS transistor MP2 and an output current of the PMOS transistor MP4 are compared by a current-mirror circuit configured with NMOS transistors MN3 and MN4, and thus a difference between the output currents are outputted as a single output voltage FOUT.
However, in the conventional D2S converter, power consumption is large in a case where a voltage swing of the single output voltage FOUT is large.
Therefore, a D2S converter having excellent duty ratio characteristics while having reduced power consumption is required.